/* specfunc/pow_int.c

 * 

 * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman

 * 

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 3 of the License, or (at

 * your option) any later version.

 * 

 * This program is distributed in the hope that it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 */

/* Author:  G. Jungman */

#include <config.h>

#include <gsl/gsl_math.h>

#include <gsl/gsl_errno.h>

#include <gsl/gsl_sf_pow_int.h>

/*-*-*-*-*-*-*-*-*-*-*-* Functions w/ Error handling *-*-*-*-*-*-*-*-*-*-*-*/

int gsl_sf_pow_int_e(double x, int n, gsl_sf_result * result)

{

  double value = 1.0;

  int count = 0;

  /* CHECK_POINTER(result) */

  if(n < 0) {

    n = -n;

    if(x == 0.0) {

      double u = 1.0 / x;

      result->val = (n % 2) ? u : (u * u) ;  /* correct sign of infinity */

      result->err = GSL_POSINF;

      GSL_ERROR ("overflow", GSL_EOVRFLW);

    }

    x = 1.0/x;

  }

  /* repeated squaring method 

   * returns 0.0^0 = 1.0, so continuous in x

   */

  do {

     if(GSL_IS_ODD(n)) value *= x;

     n >>= 1;

     x *= x;

     ++count;

  } while (n);

  result->val = value;

  result->err = 2.0 * GSL_DBL_EPSILON * (count + 1.0) * fabs(value); 

  return GSL_SUCCESS;

}

/*-*-*-*-*-*-*-*-*-* Functions w/ Natural Prototypes *-*-*-*-*-*-*-*-*-*-*/

#include "eval.h"

double gsl_sf_pow_int(const double x, const int n)

{

  EVAL_RESULT(gsl_sf_pow_int_e(x, n, &result));

}